Recently, to meet the increasing need for transmitting a large volume of data over wireless channels at high speed, intensive research is being conducted on multiple antennas technology using several antennas. Also, research on transmission diversity is being conducted to improve wireless channel capacity and reception performance in multiple antennas system.
STTD (Space Time Transmit Diversity) scheme that transmits data by using two transmission antennas and one reception antenna is a kind of transmission diversity scheme. The STTD scheme can simultaneously obtain time diversity gain and space diversity gain by transmitting the same data through two transmission antennas.
Generally, a data transmission method in which one base station (hereinafter, referred to as ‘BS’) transmits data through two transmission antenna by using the STTD scheme, is illustrated in Table 1. Specifically, the BS transmits data S1 and S2 in order through one transmission antenna and transmits data −S2* and S1* in order through the other transmission antenna. Herein, ‘*’ denotes conjugate.
TABLE 1Time tTime t + TThe first transmission antennaS1S2The second transmission antenna−S2* S1*
As illustrated in Table 1, transmission data are transmitted through the first transmission antenna and the second transmission antenna in time order after STTD encoding. In this case, data S1 and −S2* are respectively transmitted through the first and second transmission antennas at time t, and data S1* and −S2* are respectively transmitted through the first and second transmission antennas at time t+T.
Meanwhile, a multi-BS scheme in which at least two BSs transmit the same data to one mobile station (hereinafter, referred to as ‘MS’) by using the STTD scheme, has proposed.
In multi-BS scheme, adjacent BSs are set as one BS group, and the MS transmits/receives data with BSs included in the BS group simultaneously. In this case, each BS included in the BS group uses multiple antennas technology, and two or more BSs transmit the same data by using the STTD scheme. In this way, since two or more BSs transmit the same data to one MS, interference which occurs at receiving data of the MS can be decreased.
However, in case that two or more BSs transmit the same data to one MS by using STTD encoding in multi-BS scheme, there is a problem that usage efficiency of BS antennas is decreased since one transmission antenna among two or more transmission antennas of the BS is used and remainder transmission antennas of the BS are not used at transmitting data.
Therefore, there is a demand for data transmission apparatus and method which can increase usage efficiency of BS antennas and improve reception performance in multi-BS scheme.